High molecular mass, saturated hydrocarbon acid based chemical conversion coating composition

ABSTRACT

Disclosed is a method of using a high molecular mass, saturated hydrocarbon acid to generate a chemical conversion coating on light metal surfaces such as aluminum, magnesium, and titanium and their alloys.

BACKGROUND

In the metal finishing industry a chemical conversion coating is the chemical modification of the surface of a metal such that the metal in question is more resistant to oxidation or will more easily accept applied secondary coatings such as commercial paints or both.

Chemical conversion coatings have been used in the metal finishing industry for over a hundred years. In the vast majority of cases, conversion coatings are produced using inorganic chemical compounds such as chromic acid, phosphoric acid, and their corresponding inorganic salts. Chromic acid and its salts are known to cause cancer. As a result they are being phased out of the metal finishing industry. Due to governmental regulations at the state and federal levels, it is now economically unfeasible to use chromate-based conversion coating systems on light metals such as aluminum and magnesium. (In the EU, for example, the “REACH” legislation of Jun. 1, 2007, i.e., the “Registration, Evaluation, Authorisation and Restriction of Chemicals” legislation, mandates the end date for hexavalent chrome compounds as Sep. 30, 2017.) Phosphate-based systems may be used as a replacement, but the phosphate coatings are not nearly as effective as chromates. Phosphate also have environmental issues associated with their use that adds to their cost.

Various alternatives have been proposed, with limited success, including reactive coating systems using organic phosphates, organic amine phosphates, organic silicon compounds, unsaturated hydroxyl organic acids such as tannic acid, and organic nitrogen or sulfur compounds. These compounds are able to react with the base metal to modify the physical and chemical properties of the metal surface. However, they too are not nearly as cost-effective or useful as the older chromate- and phosphate-based conversion coating systems.

SUMMARY OF THE INVENTION

Low molecular mass, saturated hydrocarbon acids such as formic acid, acetic acid, and propionic acid are quite soluble in water and will form soluble salts of many metals. In contrast, higher molecular mass saturated hydrocarbon acids are far less soluble in water. It has been found that these high molecular mass organic acids chemically bond themselves to the surface of a metal in the form of an insoluble salt (rather than producing water-soluble metal salts). The resulting metal salts remain attached to the metal and modify the surface characteristics of the metal to which they are. A chemical conversion coating is formed by contacting the surface of a metal with one of these higher molecular mass organic acids and heating the metal workpiece to a temperature sufficient high to drive formation of the conversion coating.

High molecular mass saturated hydrocarbon acids are environmentally friendly and entail little or no disposal issues or work place problems. Many of these saturated acids are used in many food products or pharmacology products. Simple coatings or paints attach themselves to a given metal because of electrostatic charges or as a result of the metal's surface being mechanically or chemically etched. This is in contrast to a conversion coating, in which a chemical bond is formed between the base metal and the applied reactive material that yields the conversion coating.

Disclosed herein is a method of forming chemical conversion coatings on light metals such as aluminum, magnesium, titanium, and their alloys by the chemical reaction of high molecular mass saturated hydrocarbon organic acids with the light metal workpiece. The acids employed should have a molecular mass of at least about 340 Da. The preferred molecular mass range is from about 340 Da to about 2000 Da, and more preferably still from about 340 Da to about 1000 Da. The saturated hydrocarbon acid is applied to the metal surface to be coated, the surface is then heated to melt the hydrocarbon acid and cooled. This causes the conversion coating to form.

Thus, disclosed herein are the following:

1. A conversion coating prepared by a process comprising the steps of:

(a) contacting a substrate comprising a metal selected from aluminum, magnesium, or titanium, with a saturated hydrocarbon acid having a molecular mass of at least about 340 Da; and then

(b) heating the substrate of step (a) to a temperature at or above the melting point of the saturated hydrocarbon acid, for a time sufficient to yield a conversion coating on the substrate.

2. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 2,000 Da.

3. The conversion coating of claim 1 or 2, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 1,000 Da.

4. The conversion coating of claim 1, 2, or 3, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 70 carbon atoms.

5. The conversion coating of any one of claims 1-4, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 50 carbon atoms.

6. The conversion coating of any one of claims 1-5, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 40 carbon atoms.

7. The conversion coating of any one of claims 1-6, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 30 carbon atoms.

8. The conversion coating any one of claims 1-7, wherein the saturated hydrocarbon acid of step (a) is linear or branched.

9. The conversion coating of any one of claims 1-8, wherein the saturated hydrocarbon acid of step (a) comprises two or more fused rings.

10. A method of creating a conversion coating, the method comprising:

(a) contacting a substrate comprising a metal selected from aluminum, magnesium, or titanium, with a saturated hydrocarbon acid having a molecular mass of at least about 340 Da; and then

(b) heating the substrate of step (a) to a temperature at or above the melting point of the saturated hydrocarbon acid, for a time sufficient to yield a conversion coating on the substrate.

11. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 2,000 Da.

12. The method of claim 10 or 11, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 1,000 Da.

13. The method of claim 10, 11, or 12, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 70 carbon atoms.

14. The method of any one of claims 10-13, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 50 carbon atoms.

15. The method of any one of claims 10-14, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 40 carbon atoms.

16. The method of any one of claims 10-15, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 30 carbon atoms.

17. The method of any one of claims 10-16, wherein the saturated hydrocarbon acid of step (a) is linear or branched.

18. The method of any one of claims 10-17, wherein the saturated hydrocarbon acid of step (a) comprises two or more fused rings.

The saturated hydrocarbon acids can be purchased commercially from a number of international suppliers, including Sigma-Aldrich, St. Louis, Mo., USA. For example, 99% docosanoic acid (i.e., 99% behenic acid, m.p. ˜72 to 80° C.) is Sigma-Adrich catalog no. 216941-5G. Lithocholic acid is Sigma-Aldrich catalog no. L0720800.

The saturated hydrocarbon acid may have a linear, branched, or cyclic hydrocarbon moiety, including cyclic hydrocarbon moieties having two or more fused rings. Lithcocholic acid, for example, has a saturated hydrocarbon portion that includes four (4) fused rings. The acids are carboxylic acids and are thus “saturated” in the sense that the hydrocarbon portion of the molecule contains no double or triple bonds. The acid portion comprises a carboxylic acid—which has a single C═O unsaturation. The saturated hydrocarbon acid may include one or more acid moieties.

Numerical ranges as used herein are intended to include every number and subset of numbers contained within that range, whether specifically disclosed or not. Further, these numerical ranges should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 2 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

All references to singular characteristics or limitations of the present invention shall include the corresponding plural characteristic or limitation, and vice-versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made.

All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

The methods of the present invention can comprise, consist of, or consist essentially of the essential elements and limitations of the method described herein, as well as any additional or optional ingredients, components, or limitations described herein or otherwise useful in synthetic organic chemistry.

DETAILED DESCRIPTION OF THE INVENTION

The method proceeds as follows: A high molecular mass saturated hydrocarbon acid is applied to the metal surface to be coated, preferably an aluminum, magnesium, or titanium workpiece, or a workpiece made of an alloy of any of these metals. The hydrocarbon acid may be applied neat or dissolved/dispersed in any suitable solvent (typically water or a low molecular mass hydrocarbon such as hexane). The molecular mass of the saturated hydrocarbon acid should be at least 340 Da. Thus, the smallest saturated hydrocarbon acid employed in the method is docosanoic acid (also known as behenic acid), which has 22 carbon atoms and a molecular mass of 340.59 Da, C₂₁H₄₃COOH (CAS No. 112-85-6). Larger saturated hydrocarbon acids include, but are not limited to, C₂₃ tricosanoic acid CH₃(CH₂)₂₁COOH, C₂₄ tetracosanoic acid CH₃(CH₂)₂₂COOH, C₂₅ pentacosanoic acid CH₃(CH₂)₂₃COOH, C₂₆ hexacosanoic acid CH₃(CH₂)₂₄COOH, etc. The analogous C₇₀ saturated acid has a molecular mass of ˜1,013.85 Da. The analogous C₁₄₀ saturated acid has a molecular mass of 1,995.71 Da. The preferred molecular mass, though, of the saturated hydrocarbon acid is between about 340 Da to about 1000 Da, thus from approximately C₂₂ to approximately C₇₀ saturated organic acids.

The organic acid is applied to the metal surface to be coated. As noted above, the acid can be applied neat or dispersed/dissolved in a suitable solvent or vehicle. The metal surface is then heated to melt the applied acid, which initiates the reaction that yields the conversion coating. The workpiece is then cooled to room temperature. Any excess hydrocarbon acid is removed with a suitable cleaning agent. The result is a chemical conversion coating on the metal surface. The restulting conversion coating is resistant to alkaline cleaning solutions and stripping agents such as benzene, toluene, and the like. The following examples illustrate the process:

EXAMPLE 1

A 3 inch×4 inch (7.62 cm×10.16 cm) sample of aluminum 0.0625 inches (15.8750 mm) thick was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm²) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of stearic acid (C₁₈, molecular mass ˜284.5 Da). The sample was then gently heated until the stearic acid melted and then allowed to cool to room temperature. Any excess stearic acid was then dissolved off the sample with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal sample and the stearic acid. Treating the sample with boiling water quickly oxidized the metal surface.

EXAMPLE 2

A 3 inch×4 inch (7.62 cm×10.16 cm) sample of aluminum 0.0625 inches (15.8750 mm) thick was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm²) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of roccellic acid (C₁₇, a dibasic acid with a molecular mass ˜300.43 Da). The sample was gently heated until the roccellic acid melted and cooled to room temperature. Any excess roccellic acid was then dissolved off the metal surface with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the roccellic acid. Treating with boiling water oxidized the metal surface.

EXAMPLE 3

A 3 inch×4 inch (7.62 cm×10.16 cm) sample of aluminum 0.0625 inches (15.8750 mm) thick was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm²) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of docosanoic acid (C₂₂, molecular mass ˜340.57 Da). The sample was then gently heated to melt the docosanoic acid and allowed to cool to room temperature. Any excess docosanic acid was then dissolved off the metal sample with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating that a chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 4

An aluminum sample was prepared as described previously. The sample was then coated with a thin film of lithocholic acid (C₂₄, molecular mass ˜376.58 Da):

The sample was gently heated until the lithocholic acid melted and cooled to room temperature. Excess lithocholic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the sample and an increase in the thickness of the sample, indicating that a chemical reaction had taken place between the metal and the lithocholic acid. Water beaded when applied to the surface of the sample. Treating with boiling water did not oxidize the metal.

EXAMPLE 5

An aluminum sample was prepared as described previously. The sample was then coated with a thin film of deoxycholic acid (C₂₄, molecular mass ˜392.58):

The sample was then heated to melt the deoxycholic acid and allowed to cool to room temperature. Any excess material was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating that a chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 6

An aluminum sample was prepared as described previously. The sample was then coated with a thin film of a synthetic saturated hydrocarbon acid (molecular mass ˜700 Da). and then heated to its melting point and then allowed to cool below its melting point. Any excess acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 7

An aluminum sample was prepared as described previously. The sample was then coated with a thin film of a synthetic saturated hydrocarbon wax acid (molecular mass ˜993 Da). The sample was heated until the wax melted and was then cooled to room temperature. Any excess was was then dissolved off the metal with benzene followed by cleaning the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the sample and the thickness of the sample, indicating that a chemical reaction had taken place between the metal and the organic wax. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 8

A 3 inch×8 inch (7.62 cm×20.32 cm) aluminum alloy 5052, 0.030 inches (0.76 mm) was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm²) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of stearic acid (molecular mass ˜284.5 Da). The sample was gently heated until the stearic acid melted allowed to cool to room temperature. Any excess stearic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the stearic acid. Treating the sample with boiling water caused oxidation of the surface.

EXAMPLE 9

A sample was prepared as in Example 8 and coated with a thin film of heneicosanoic acid (molecular mass ˜326.56 Da). The sample was then heated to melt the acid and allowed to cool to room temperature. Any excess heneicosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the heneicosanoic acid. Treating the sample with boiling water caused oxidation of the surface.

EXAMPLE 10

A sample was prepared as in Example 8 and then coated with a thin film of docosanoic acid (molecular mass ˜340.38). The sample was heated to melt the acid and allowed to cool to room temperature. Any excess docosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place between the metal and the organic acid. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 11

A sample was prepared as in Example 8 and then coated with a thin film of a synthetic saturated hydrocarbon acid having a molecular mass of ˜700 Da. The sample was then heated to melt the hydrocarbon and allowed to cool to room temperature. Any excess hydrocarbon acid was then dissolved from the sample surface with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating that a chemical reaction had taken place between the metal and the hydrocarbon acid. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 12

A 2 inch×2 inch (5.08 cm×10.16 cm) sample of magnesium 0.035 inches (0.889 mm) thick was made the cathode in a electrochemical cell consisting of 5% potassium hydroxide in distilled water solution at twelve volts and thirty amps per square foot for 30 seconds to remove any existing soil and/or existing oxides from the sample, rinsed in distilled water, dried, weighed and then coated with a thin film of a synthetic saturated hydrocarbon acid (molecular mass ˜700 Da). The sample was then heated to melt the hydrocarbon acid and allowed to cool to room temperature. Any excess hydrocarbon acid was then dissolved off the metal with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 13

A sample was prepared as in Example 12 and then coated with a thin film of roccellic acid (molecular mass ˜300.43 Da). The sample was heated to melt the roccellic acid and allowed to cool to room temperature. Any excess roccellic acid was then dissolved off the metal with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the organic acid in question. Treating the sample with boiling water quickly oxidized it.

EXAMPLE 14

A sample was prepared as in Example 12 and then coated with a thin film of heneicosanoic acid (molecular mass ˜326.56), then heated to its melting point and allowed to cool to room temperature. Any excess heneicosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the organic acid in question. Treating with boiling water quickly oxidized the sample surface.

EXAMPLE 15

A sample was prepared as in Example 12 and then coated with a thin film of docosanoic acid. The sample was then heated to melt the acid and allowed to cool to room temperature. Any excess docosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 16

A 4 inch×4.5 inch (10.16 cm×11.43) sample of magnesium alloy “AZ91 D” 0.035 inches thick was made the cathode in a electrochemical cell consisting of 5% percent potassium hydroxide in distilled water solution at twelve volts and thirty amps per square foot for 30 seconds to remove any existing soil and/or existing oxides from the metal's surface, rinsed in distilled water, dried, weighed and then coated with a thin film of a synthetic saturated hydrocarbon acid (molecular mass ˜700 Da). The sample was then heated melt the hydrocarbon and cooled to room temperature. Any excess hydrocarbon acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 17

A sample was prepared as in Example 16 and then coated with a thin film of stearic acid (molecular mass ˜284.5). The sample was the heated to melt the stearic acid and allowed to cool to room temperature. Any excess stearic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place. Treating with boiling water quickly oxidized the metal.

EXAMPLE 18

A sample was prepared as in Example 16 and then coated with a thin film of a synthetic saturated hydrocarbon wax acid (molecular mass ˜993). The sample was heated to melt the wax and then cooled to room temperature. Any excess wax was then dissolved off the metal with benzene followed by cleaning the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface. 

What is claimed is:
 1. A conversion coating prepared by a process comprising the steps of: (a) contacting a substrate comprising a metal selected from aluminum, magnesium, or titanium, with a saturated hydrocarbon acid having a molecular mass of at least about 340 Da; and then (b) heating the substrate of step (a) to a temperature at or above the melting point of the saturated hydrocarbon acid, for a time sufficient to yield a conversion coating on the substrate.
 2. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 2,000 Da.
 3. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 1,000 Da.
 4. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 70 carbon atoms.
 5. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 50 carbon atoms.
 6. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 40 carbon atoms.
 7. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 30 carbon atoms.
 8. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) is linear or branched.
 9. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) comprises two or more fused rings.
 10. A method of creating a conversion coating, the method comprising: (a) contacting a substrate comprising a metal selected from aluminum, magnesium, or titanium, with a saturated hydrocarbon acid having a molecular mass of at least about 340 Da; and then (b) heating the substrate of step (a) to a temperature at or above the melting point of the saturated hydrocarbon acid, for a time sufficient to yield a conversion coating on the substrate.
 11. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 2,000 Da.
 12. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 1,000 Da.
 13. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 70 carbon atoms.
 14. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 50 carbon atoms.
 15. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 40 carbon atoms.
 16. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 30 carbon atoms.
 17. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) is linear or branched.
 18. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) comprises two or more fused rings. 